The present invention relates to a method and an apparatus for automatic focusing of every image point in an image in a system in which the image is being observed by means of an objective.
In the manufacture and evaluation of multiphase substances, such as, for example, nuclear fuel plates made of mixtures of uranium dioxide and plutonium dioxide, as they are used, for example, for fast breeder reactors, or in the case of plutonium recovery for light water reactors, the distribution of the, e.g., plutonium is different in each manufacturing process. In the case where the manufacturing process or treatment of a starting powder does not impose substantial mixed crystal formation, the plutonium distribution may become inhomogeneous. In such a case there is a need for the manufacturer to learn how the plutonium is distributed in order to draw conclusions therefrom regarding the manufacturing process. The fuel customer, on the other hand, wants to know whether the plutonium in the plates is indeed present in the required homogeneous distribution. If, now, homogeneity or the distribution of a second phase is to be quantified, it is the general practice to utilize the deviation of the concentration from a given standard or a distribution parameter derived therefrom as the measuring index.
If during automatic image analysis more than one sample point is to be examined, it is necessary to displace the sample. It is then assumed that the sample remains continuously at the same distance in front of the objective lens of an observation microscope or of a television camera. If this is not the case with certainty, the image will be out of focus and thus the measuring result will be wrong. To prevent this, the image must be refocused again and again.